Attenuator for millimeter and submillimeter wavebands of electromagnetic radiation

ABSTRACT

An attenuator for millimeter and submillimeter wavebands of electromagnetic radiation, comprising at least three reflectors each of which is made as a series of parallel conductors the shortest distance between which is less than the wavelength of the selected electromagnetic radiation and which are secured on a common frame, the reflectors being positioned in non-parallel planes and provided with means allowing them to rotate about the attenuator axis, while the attenuation factor is determined by the angle between the respective conductors of adjacent reflectors.

United States Patent Vinogradov et al.

[54] ATTENUATOR FOR MILLIMETER AND SUBMILLIMETER WAVEBANDS OF ELECTROMAGNETIC RADIATION [72] lnventors: Evgeny Alexandrovich Vinogradov, Kozhevnicheskaya ulitsa, lb, kv. 33; Nataliya Alexandrovna lrisova, ulitsa Vavilova, 44, korpus 4, kv. 74, both of Moscow, U.S.S.R.

[22] Filed: June 29, 1970 [21] Appl. No.: 50,432

[52] US. Cl. ..333/81 R, 333/98 R [51] Int. Cl. ..H0lp 1/22 [58] Field of Search .-..333/21 A, 81, 81 B, 98 M;

[56] References Cited UNITED STATES PATENTS 2,554,936 5/1951 Burtner ..343/756 [151 3,693,l 16 [4 1 Sept. 19, 1972 2,603,709 7/1952 Bowen ..333/8l B 2,603,710 7/1952 Bowen ..333/8l B 2,943,175 6/1960 Guanellaa ..333/2l A X 3,431,044 3/1969 Clark ..350/159 X Primary Examiner-Paul L. Gensler Attorney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT An attenuator for millimeter and submillimeter wavebands of electromagnetic radiation, comprising at least three reflectors each of which is made as a series of parallel conductors the shortest distance between which is less than the wavelength of the selected electromagnetic radiation and which are secured on a common frame, the reflectors being positioned in nonparallel planes and provided with means allowing them to rotate about the attenuator axis, while the attenuation factor is determined by the angle between the respective conductors of adjacent reflectors.

4 Claims, 3 Drawing Figures ATTENUATOR FOR MILLIMETER AND SUBMILLIMETER WAVEBANDS OF ELECTROMAGNETIC RADIATION space, which are designed around two total internal l5 reflection lenses.

The lenses are placed at a certain distance from each other and such that their identical facets are parallel. If the distance between the lenses is sufficiently large, the electromagnetic radiation striking the first lens will be totally internally reflected and will leave the lens at a right angle to its initial direction of propagation. If the parallel facets of the two lenses are moved closer to each other, a portion of the electromagnetic energy will pass through both lenses. This portion of the energy will leave the second lens in a direction corresponding to that of the incident electromagnetic radiation.

The smaller the gap between the parallel facets of the lenses and the greater the wavelength of the electromagnetic radiation, the less is the attenuation of the electromagnetic power obtained with the use of such a lens attenuator.

However, attenuators known in the art suffer from considerable disadvantages. For instance, they have a high value of initial attenuation of electromagnetic radiation (when there is no gap between the lenses at all) due to its being absorbed in the bulk of the dielectric material and reflected from the facets of the lens. Also, the attenuation of these devices depends upon the wavelength of the electromagnetic radiation, which makes it difficult to calibrate such an attenuator and employ it in a broad frequency range.

Additionally, the latter effect limits the possibilities of using this attenuator when operating with converging or diverging beams of electromagnetic radiation.

It is also necessary to point out that the factor of electromagnetic power attenuation of the known attenuator is highly dependent on the angle of incidence of the electromagnetic radiation (in so far as the law of total internal reflection may not be observed at all at certain angles of incidence of the electromagnetic radiation).

An object of the invention is to provide a wideband attenuator for millimeter and submillimeter waves of electromagnetic radiation.

The invention contemplates an attenuator for millimeter and submillimeter wavebands of electromagnetic radiation, which, according to the invention,

comprises at least three reflectors, each designed as a series of mutually parallel conductors fixed on a common frame, the shortest distance between the conductors being less than the wavelength of the chosen electromagnetic radiation band, the reflectorsbeing positioned so as to be in non-parallel planes and provided with a means allowing them to rotate about the axis of the attenuator, the attenuation factor being determined by the angle between conductors of adjacent reflectors.

It is preferred that an odd-number of reflectors is mounted so that the projections of their conductors onto a plane normal to the attenuator s axis are parallel to one another.

The invention will be better understood from the description of an embodiment given by way of example with reference to the accompanying drawings in which:

FIG. 1 is a diagram showing the positions of at least three reflectors of the attenuator;

FIG. 2 is an exemplary form of a reflector, according to the invention; and

FIG. 3 is the attenuator design according to the inventlon.

The illustrated attenuator for submillimeter and millimeter wavebands of electromagnetic radiation comprises at least three reflectors 1, 2, 3 (FIG. 1) whose planes are non-parallel to each other to exclude possible resonance effects.

Each reflector is a frame 4 (FIG. 2) made, for instance, as a circle. Stretched over the frame are conductors 5 which are parallel to one another.

To reduce diffraction effects in the attenuator, diameter a of the frame 4 should exceed the maximum wavelength A of the selected band.

To reduce resistance losses, it is advisable that the conductors 5 stretched over the frame 4 be made of a metal having maximum conductivity or that a metal coating be used having a thickness which exceeds that of the skin-layer in the selected waveband. The cross section of the conductors 5 may be of any shape.

The distance 1 between the conductors 5 is selected to be less than the maximum wavelength of the electromagnetic radiation in the given range.

The higher the ratios M! and d/A where d is the width of a conductor in the plane of the frame, the higher is the maximum value of the attenuation factor that can be obtained in a particular design of the attenuator.

One form of the attenuator design is presented in FIG. 3. The reflectors 1, 2, 3 made as described above are housed in a support or casing 6 of the attenuator which can rotate about its longitudinal axis with the help of a worm gear 7. The reflectors 1 and 3 are mounted in the case 6 so that the projections of their conductors on a plane normal to the attenuators axis are parallel to one another. The planes of the reflectors 1, 2, 3 are skewed with respect to the casing 6 as explained for FIG. 1. The reflector 2 is fixed in a ring 8 which is coupled to a worm gear 9 which allows the reflector 2 to be rotated with respect to the axis of the casing 6 and the reflectors 1; 3 through an angle of not less than The reflector 2 is fixed in the ring 8 in such a way that when the latter is in one extreme position the projections of the conductors of the reflector 2 on the plane normal to the attenuator axis are parallel to the projections of the conductors of the reflectors l and 3 on the same plane, and when it is in the opposite extreme position the respective projections are normal to each other. The ring 8 is provided with a device for monitoring the angle of rotation of the reflector 2 with respect to the axis of the casing 6.

The device operates in the following way.

The electromagnetic radiation propagation in free space, which is to be attenuated, is directed along the axis of the attenuator towards the reflector l. The worm gear 9 is used to adjust the projections of the conductors of the reflector 2 on the plane normal to the attenuator axis so that they are parallel to the projections of the conductors of the reflectors l and 3. When the reflectors are set in such positions the attenuator forms a polarization filter having a maximum transmission factor (approaching unity) for the polarization component of the electromagnetic radiation, the vector E of the electrical field strength of the component being at a right angle to the projections of the conductors of the reflectors l, 2 and 3 on the plane normal to the attenuator axis.

Polarization components having other directions of the electrical field strength vector, if any, are reflected by the attenuator at a certain angle with respect to the attenuator axis due to the fact that the planes of the reflectors are skewed with respect to the reflector axis.

The reflected radiation can be either absorbed in the walls of the casing 6 with the use of a special absorber or simply allowed to disperse in free space. If the worm gear 9 turns the reflector 2, the power transmission factor of the attenuator will be reduced while the direction of polarization of the radiation that has passed through the attenuator will remain unchanged.

In a general case, the attenuation factor is determined by the angle between the respective conductors of the adjacent reflectors and can be calculated quite accurately with the help of exact theoretical formulas which take into account the parameters and positions of the reflectors.

Further, the attenuation factor is independent, within a broad range, of the wavelength of the electromagnetic radiation which makes it possible to employ the attenuator, for instance, as a neutral attenuating means in the circuits of two-beam millimeter and submillimeter spectrometers.

The angle of incidence at which the electromagnetic radiation strikes the attenuator can vary within quite a broad range. The attenuator can operate with both converging and diverging beams of electromagnetic radiation. The minimum initial power attenuation produced by the attenuator in a polarization component of the electromagnetic radiation with a previously selected direction of polarization can be lower than 0.1 db and does not depend on the aperture of the attenuator.

The maximum attenuation can exceed 40 db.

What is claimed is:

1. An attenuator for millimeter and submillimeter wavebands of electromagnetic radiation, comprising elongated support means defining a longitudinal axis for the attenuator, at least three reflectors positioned in said support means in spaced-apart relation, in nonparallel planes generally transverse of the attenuator axis, means to rotate said reflectors together about the attenuator axis, each reflector including a plurality of substantially parallel conductors, the shortest distance between the latter being less than the maximum wavelength of the selected electromagnetic radiation band, a frame to which said conductors are secured, and means to rotate at least on intermediate one of said reflectors with respect to the attenuator axis by at least the attenuator having an attenuation factor determined by the angle between said conductors on adacent ones of sai reflectors but free from rotation of the polarization plane.

2. The attenuator as claimed in claim 1 wherein said reflectors are provided in an odd number so that the projections of said conductors of the odd-numbered reflectors, on planes normal to the attenuator axis, are parallel to each other.

3. An attenuator as claimed in claim 1 wherein said frames are circular.

4. The attenuator as claimed in claim 3 wherein said frames have a diameter exceeding said maximum wavelength of the selected band. 

1. An attenuator for millimeter and submillimeter wavebands of electromagnetic radiation, comprising elongated support means defining a longitudinal axis for the attenuator, at least three reflectors positioned in said support means in spaced-apart relation, in non-parallel planes generally transverse of the attenuator axis, means to rotate said reflectors together about the attenuator axis, each reflector including a plurality of substantially parallel conductors, the shortest distance between the latter being less than the maximum wavelength of the selected electromagnetic radiation band, a frame to which said conductors are secured, and means to rotate at least on intermediate one of said reflectors with respect to the attenuator axis by at least 90*, the attenuator having an attenuation factor determined by the angle between said conductors on adjacent ones of said reflectors but free from rotation of the polarization plane.
 2. The attenuator as claimed in claim 1 wherein said reflectors are provided in an odd number so that the projections of said conductors of the odd-numbered reflectors, on planes normal to the attenuator axis, are parallel to each other.
 3. An attenuator as claimed in claim 1 wherein said frames are circular.
 4. The attenuator as claimed in claim 3 wherein said frames have a diameter exceeding said maximum wavelength of the selected band. 